package com.zksy.common.netty;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
import java.util.List;

/** 每条连接独立累积报文；校验失败只丢弃坏帧，不关闭设备连接。 */
public final class DeviceFrameDecoder extends ByteToMessageDecoder {
    public enum Protocol { PINGSHENG, MANHOLE, GAS, FIRE_PRESSURE }
    private static final int MAX_FRAME = 8192;
    private final Protocol protocol;

    public DeviceFrameDecoder(Protocol protocol) { this.protocol = protocol; }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {
        int minimum = protocol == Protocol.MANHOLE ? 72 : protocol == Protocol.GAS ? 74 : 5;
        while (in.readableBytes() >= minimum) {
            int start = in.readerIndex();
            int length;
            if (protocol == Protocol.PINGSHENG) {
                if (in.getUnsignedMedium(start) != 0x123456) { in.skipBytes(1); continue; }
                length = in.getUnsignedShort(start + 3);
                if (length < 10 || length > MAX_FRAME) { in.skipBytes(1); continue; }
                if (in.readableBytes() < length) {
                    // 长度字段损坏时，寻找后续完整且两层校验通过的上报帧。
                    int next = nextPingshengFrame(in, start + 3);
                    if (next < 0) return;
                    in.readerIndex(next);
                    continue;
                }
                int xor = 0;
                for (int i = 0; i < length; i++) xor ^= in.getUnsignedByte(start + i);
                if (xor != 0) { in.skipBytes(1); continue; }
            } else if (protocol == Protocol.MANHOLE) {
                // 当前井盖解析器：35字节参数 + 20字节SIM + 15字节IMEI + CRC16。
                length = 72;
                if (crc(in, start, 70) != in.getUnsignedShortLE(start + 70)) { in.skipBytes(1); continue; }
            } else if (protocol == Protocol.GAS) {
                // 当前已支持的7指标上报结构固定为74字节，内外两层校验与接收器一致。
                length = 74;
                if (in.getUnsignedByte(start) != 0x7E || in.getUnsignedByte(start + 15) != 0xAA
                        || !gasChecksum(in, start)) { in.skipBytes(1); continue; }
            } else {
                if (in.getUnsignedShort(start) != 0x7E7E) { in.skipBytes(1); continue; }
                // 现有消防设备长度字段不作为可信边界，使用结束符 + 完整CRC确认边界。
                // 不能单靠03分隔：日期、TLV和压力数据中也可能出现03。
                length = fireLength(in, start);
                if (length == 0) {
                    // 坏帧后可能紧接新报文，不能让坏CRC永久阻塞下一条有效数据。
                    boolean recovered = false;
                    for (int next = start + 2; next + 16 < in.writerIndex(); next++) {
                        if (in.getUnsignedShort(next) == 0x7E7E && fireLength(in, next) > 0) {
                            in.readerIndex(next);
                            recovered = true;
                            break;
                        }
                    }
                    if (recovered) continue;
                    if (in.readableBytes() >= MAX_FRAME) { in.skipBytes(1); continue; }
                    return;
                }
            }
            out.add(in.readRetainedSlice(length));
        }
    }

    private static boolean gasChecksum(ByteBuf in, int start) {
        int body = 0, full = 0;
        for (int i = 16; i < 72; i++) body += in.getUnsignedByte(start + i);
        for (int i = 3; i < 73; i++) full += in.getUnsignedByte(start + i);
        return (body & 255) == in.getUnsignedByte(start + 72)
                && ((255 - full) & 255) == in.getUnsignedByte(start + 73);
    }

    private static int nextPingshengFrame(ByteBuf in, int from) {
        for (int start = from; start + 10 <= in.writerIndex(); start++) {
            if (in.getUnsignedMedium(start) != 0x123456) continue;
            int length = in.getUnsignedShort(start + 3);
            if (length < 14 || length > MAX_FRAME || start + length > in.writerIndex()
                    || in.getUnsignedByte(start + 6) != 0x31) continue;
            int xor = 0;
            for (int i = 0; i < length; i++) xor ^= in.getUnsignedByte(start + i);
            if (xor != 0) continue;
            int src = (in.getUnsignedByte(start + 7) + 1) / 2;
            int destIndex = start + 8 + src;
            if (src == 0 || src > 10 || destIndex >= start + length - 3) continue;
            int dest = (in.getUnsignedByte(destIndex) + 1) / 2;
            int body = destIndex + 1 + dest;
            if (dest > 10 || body + 2 >= start + length - 3) continue;
            if (crc(in, body, start + length - 3 - body) == in.getUnsignedShortLE(start + length - 3)) return start;
        }
        return -1;
    }

    private static int fireLength(ByteBuf in, int start) {
        if (in.writerIndex() - start < 14) return 0;
        if (in.getUnsignedByte(start + 10) != 0xEF) {
            // 上报数据固定头之后按TLV跨过值区，值中偶然的03+CRC不能作为帧尾。
            int cursor = start + 37;
            int limit = Math.min(in.writerIndex(), start + MAX_FRAME);
            while (cursor + 3 <= limit) {
                int marker = in.getUnsignedByte(cursor);
                if (marker == 0x03 || marker == 0x17) {
                    return crc(in, start, cursor - start + 1) == in.getUnsignedShort(cursor + 1)
                            ? cursor - start + 3 : 0;
                }
                int tag = in.getUnsignedShort(cursor);
                int bytes = (in.getUnsignedByte(cursor + 2) >>> 3) & 31;
                if (bytes == 0 && tag == 0x581A) bytes = 2;
                if (bytes == 0 && tag == 0x4520) bytes = 4;
                cursor += 3 + bytes;
            }
            return 0;
        }
        int value = 0xFFFF;
        int end = Math.min(in.writerIndex() - 2, start + MAX_FRAME - 2);
        for (int i = start; i < end; i++) {
            value = crcByte(value, in.getUnsignedByte(i));
            int marker = in.getUnsignedByte(i);
            // 消防现有crc16Tall以高字节在前追加CRC。
            if (i >= start + 14 && (marker == 0x03 || marker == 0x17)
                    && value == in.getUnsignedShort(i + 1)) return i - start + 3;
        }
        return 0;
    }

    private static int crc(ByteBuf in, int start, int length) {
        int value = 0xFFFF;
        for (int i = 0; i < length; i++) value = crcByte(value, in.getUnsignedByte(start + i));
        return value;
    }

    private static int crcByte(int value, int b) {
        value ^= b;
        for (int i = 0; i < 8; i++) value = (value & 1) == 1 ? (value >>> 1) ^ 0xA001 : value >>> 1;
        return value;
    }
}